Nanofibers are applied to the fields demanding optical characteristics such as high transparency, where the nano-size effect of nanofibers are taken advantage of. For example, transparent fabric may be made of nanofibers with a diameter reduced to or below the wavelength of visible light. By the use of nanofibers the diameter of which is equal to the wavelength of visible light, structural color may be exhibited. Nanofibers also find applications in the fields demanding superabsorbent characteristics or high surface activity, where the super-specific surface area effect of nanofibers is taken advantage of, and in the fields demanding mechanical characteristics such as tensile strength and electrical characteristics such as high conductivity, where the supramolecular arrangement effect of nanofibers is made use of Nanofibers having such characteristics have been used in the form of, for example, not only single fibers but aggregates (i.e., fabrics) or composites.
Embodiments of nanofibers that have been proposed include nanoscale polysaccharide fibers of 500 nm or smaller in diameter, made mainly of polysaccharides, and obtained by electrospinning (see patent literature 1 below). According to the disclosure of patent literature 1, the fibers are useful as a living tissue culture substratum in regenerative medicine or a part of a biomaterial, such as artificial valves, artificial organs, artificial vessels, and wound dressings, aiming at repair, regeneration, or treatment of living tissue deficiency.
A cosmetic sheet comprising a network structure made of a polymer nanofiber and a cosmetic or a cosmetic component held in the network structure has been proposed in patent literature 2 below. Patent literature 2 alleges that the cosmetic sheet has not only improved adhesion or comfort to the user's face, hand, or leg but also improved preservability.
The sheets made of the nanofibers described in patent literatures cited above have low stiffness due to the fineness of the nanofibers and cannot be said to have good handling properties. Furthermore, they are not designed to be transferred easily.
Apart from these techniques, known techniques relating to sheets containing electrospun nanofibers include those of patent literatures 3 and 4 shown below. However, when the sheet obtained in accordance with the techniques disclosed is applied to the surface of an object, for example, human skin, it is liable to fail to maintain the fibrous form or come off due to poor adhesion. To enhance the adhesion, a pressure sensitive adhesive layer might be provided on one side of the sheet, but the adhesive layer is apt to stick to itself because the sheet per se is very thin and make the sheet difficult to handle. Furthermore, when the sheet is applied to the skin, the sheet tends to lift from the skin. To improve the handling properties, a gel may be used as a material of the adhesive layer to increase the stiffness of the sheet, in which case, however, the sheet will have an increased thickness and reduced comfort to the skin when worn.